1. Field of the Invention
The present invention relates to a centrifugal clutch, more particularly to a starting clutch for a vehicle, and to an improvement of the clutch for eliminating the trouble arising from a deficiency in capacity of the clutch which is generated due to a modification to the vehicle, such an increase in engine output or an increase in exhaust gas quantity.
2. Description of Background Art
A centrifugal clutch for starting of a vehicle is connected directly to a crankshaft of an engine, and has a structure in which attendant on the rotation of the crankshaft, a plurality of clutch weights of the centrifugal clutch are inclined outwards against a spring force by the action of centrifugal forces, and a lining portion at an outer circumferential portion of the clutch weights is brought into contact with and engaged with an inner circumferential portion of a clutch outer, whereby the power of the crankshaft is transmitted from the clutch outer through a driving gear, a driven gear and a speed change clutch to a main shaft of a transmission mechanism. Such a centrifugal clutch is conventionally well known, as one example thereof is described in Japanese Patent Publication No. Sho 63-27586.
As shown in FIGS. 8 and 9, each clutch weight 02 of the centrifugal clutch 010 has a structure in which a plurality of sheets of weight component members 02X formed in a predetermined shape by baking an appropriate sintered metallic powder are united by stacking them and fixing them together by an appropriate means, and a lining member (portion) 02a is adhered to an outer circumferential portion of the united body. Alternatively, each clutch member 02 has a structure in which a plurality of sheets of weight component members 02X formed by stamping an appropriate steel sheet such as an SP material (e.g., a hard metal) in a predetermined shape are united by stacking them and fixing them together by an appropriate means such as welding, and a lining (portion) member 02a is adhered to an outer circumferential portion of the united body. In any case, the weight component member 02X is composed of a single member.
Meanwhile, when a modification for an increase in engine output or an increase in engine exhaust gas quantity in a vehicle is contrived, it is supposed that the centrifugal clutch for the starting that has been used hitherto is used as it is. In this case, attendant on the modification for an increase in the engine output or an increase in the exhaust gas quantity, the capacity of the centrifugal clutch becomes deficient, and the matching property thereof is lost, resulting in that a stagger is generated in the engaging timing (stall) of the clutch or the like due to the deficiency in the capacity.
For example, when the power of an engine with a higher output is transmitted by a centrifugal clutch with the same capacity, the centrifugal force generated in the weight is the same at a minimum engine rotation frequency at which the power has been perfectly transmitted where the centrifugal clutch has been used for an engine with a lower output, but, under the higher engine output, the centrifugal clutch is not perfectly engaged and a slip is generated therein. Therefore, for perfect engagement of the clutch, the engine rotational frequency must be increased, resulting in that it takes a longer time until the clutch connection is made, the efficiency of the process from starting to normal running is lowered, and fuel consumption becomes worse.
Since the stagger in the engaging timing of the clutch is attributable to the structure and function of the centrifugal clutch themselves, the above-mentioned problems cannot be dissolved without a structural modification such as an increase of the clutch capacity.
Accordingly, a structural modification for increase the capacity of the centrifugal clutch attendant on the modification for an increase in engine output or in engine exhaust gas quantity, i.e., a structural modification consisting in an increase of clutch capacity for matching the engaging timing of the centrifugal clutch attendant on the modification of engine performance, is indispensable.
As a structural modification for an increase in the capacity of the centrifugal clutch according to the background art, a structural modification consisting in a change in the outer shape of the clutch weight itself such as an increase of the width of a tip portion of the clutch weight or a change of the thickness thereof has been principally adopted.
The structural modification can be said to be a natural choice, in view of the fact that the base material of the conventional clutch weight is a single material such as an SP material or is formed by baking a single sintered metallic powder.
However, the structural modification consisting in a change of the outer shape of the clutch weight member for the modification of the capacity of the centrifugal clutch leads to an increase in the size of the centrifugal clutch, which is not an appropriate selection in view of the arrangement of the clutch in a limited space. Namely, adoption of the structural modification consisting in modifying the outer shape of the weight member is not an appropriate selection, since it leads to a change in the surrounding structure for securing a space necessary for coping with the increase in the clutch size and the change of the surrounding structure is expensive.
Accordingly, there is a demand for an appropriate measure of increasing the clutch capacity for solving the problems such as a stagger in the engaging timing of the centrifugal clutch generated attendant on an increase in engine output or in engine exhaust gas quantity, without increasing the size of the centrifugal clutch.